Arrangement for mirror temperature measurement and/or thermal actuation of a mirror in a microlithographic projection exposure apparatus

ABSTRACT

The disclosure concerns an arrangement for mirror temperature measurement and/or thermal actuation of a mirror in a microlithographic projection exposure apparatus. The mirror has an optical effective surface and at least one access passage extending from a surface of the mirror, that does not correspond to the optical effective surface, in the direction of the effective surface. The arrangement is designed for mirror temperature measurement and/or thermal actuation of the mirror via electromagnetic radiation which is propagated along the access passage. The electromagnetic radiation is reflected a plurality of times within the access passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35 USC120 to, International Application Serial Number PCT/EP2011/0066415,filed Sep. 21, 2011, which claims benefit under 35 USC 119 of GermanPatent Application 10 2010 041 500.6, filed Sep. 28, 2010. InternationalApplication Serial Number PCT/EP2011/0066415 also claims priority under35 USC 119 to U.S. Provisional Application No. 61/387,075, filed Sep.28, 2010. The entire contents of each of these applications are herebyincorporated by reference.

FIELD

The disclosure concerns an arrangement for mirror temperaturemeasurement and/or thermal actuation of a mirror in a micro lithographicprojection exposure apparatus.

BACKGROUND

Microlithography is used for the production of micro structuredcomponents such as for example integrated circuits or LCDs. Themicrolithography process is carried out in a so-called projectionexposure apparatus having an illumination system and a projectionobjective. The image of a mask (=reticle) illuminated via theillumination system is projected via the projection objective onto asubstrate (for example a silicon wafer) which is coated with alight-sensitive layer (photoresist) and arranged in the image plane ofthe projection objective in order to transfer the mask structure ontothe light-sensitive coating on the substrate.

Mirrors are used as optical components for the imaging process inprojection objectives designed for the EUV range, that is to say atwavelengths of for example about 13 nm or about 7 nm, due to the generallack of availability of suitable translucent refractive materials. Aproblem which arises in practice is that the EUV mirrors experience arise in temperature and therefore a thermal expansion or deformation, asa consequence of absorption of the radiation emitted by the EUV lightsource. That expansion or deformation in turn can result in worsening ofthe imaging properties of the optical system. To assess those effectsand possibly to be able to compensate for them, it is desirable todetermine the extent of that rise in mirror temperature as accurately aspossible and possibly control it in the sense of thermal actuation. Afurther problem can arise because, by virtue of using specialillumination settings (such as for example dipole or quadrupolesettings) in the lithography process and by virtue of the diffractionorders caused by the reticle, the heat input caused by the EUV radiationcan vary over the optically effective cross-section of mirrors near thepupil, that is to say that it involves non-homogenous heat input intothe mirror. In addition field variations in the reticle and/or partialmasking off of the full field can result in non-homogenous lightintensities on mirrors near the field.

Approaches for mirror temperature measurement and/or actuation of amirror or targeted deformation thereof are known, for example, from WO2010/018753 A1, US 2004/0051984 A1, WO 2008/034636 A2, DE 10 2009 024118 A1 and WO 2009/046955 A2.

SUMMARY

The disclosure provides an arrangement for mirror temperaturemeasurement and/or for thermal actuation of a mirror in amicrolithographic projection exposure apparatus, which permits rapid andreliable mirror temperature measurement or thermal actuation withoutadversely affecting the lithography process.

In one aspect, the disclosure provides an arrangement for mirrortemperature measurement and/or thermal actuation of a mirror in amicrolithographic projection exposure apparatus the mirror has anoptical effective surface and at least one access passage extending froma surface of the mirror, that does not correspond to the opticaleffective surface, in the direction of the effective surface. Thearrangement is designed for mirror temperature measurement and/orthermal actuation of the mirror via electromagnetic radiation which ispropagated along the access passage. The electromagnetic radiation isreflected a plurality of times within the access passage.

The disclosure is therefore based on the concept of implementing amirror temperature measurement and/or thermal actuation of a mirror in amicro lithographic projection exposure apparatus by way of an accesspassage which extends from a surface other than the optical effectivesurface of the mirror into the mirror substrate. By virtue of thataccess passage the electromagnetic radiation serving for mirrortemperature measurement and/or thermal actuation can be “read off” (inthe case of mirror temperature measurement) or (in the case of thermalactuation) passed into the mirror substrate material, without adverselyaffecting the optical effective surface of the mirror but in theimmediate proximity with that optical effective surface.

The disclosure makes use in particular of the fact that theelectromagnetic radiation reflected within the access passage, withsufficiently shallow reflection angles, that is to say in situationsinvolving what is referred to as “grazing incidence”, is determined onlywith respect to a very slight or negligible proportion by the emissivityor absorption of the wall or surface causing the reflection within theaccess passage. Rather, with such grazing incidence within the accesspassage the situation involves substantially a (forwards) transport ofthe electromagnetic radiation along the access passage so that therespective reflecting wall of the access passage itself only has aslight or negligible radiation contribution.

Consequently, in the case of mirror temperature measurement theelectromagnetic radiation can be transported from the location at whichthe radiation is read off or from a region in the immediate proximity ofthe optical effective surface of the mirror by way of the access passageto a sensor disposed outside the mirror substrate in order to obtaininformation about the temperature state of the optical effective surfaceof the mirror by way of measurement and evaluation which is effectedoutside the mirror substrate, and optionally to provide for effectiveregulation of the mirror temperature.

Conversely, in the case of thermal actuation, it is possible to providefor specifically targeted and controlled coupling of electromagneticradiation by way of the access passage into a region in the immediateproximity of the optical effective surface, in which case thatspecifically targeted and controlled introduction of electromagneticradiation can be combined with permanent heat dissipation by way ofsuitable cooling, in particular—as described in greater detailhereinafter—in a manner which is advantageous in terms of regulatingprocedures.

In an advantageous configuration the reflection angle of theelectromagnetic radiation within the access passage is not greater than20°, preferably not greater than 15°, whereby the above-described“grazing incidence” is afforded.

In that respect the reflection angle is interpreted here and hereinafteras the angle of the incident and reflected beam relative to thereflecting surface.

To ensure that all electromagnetic radiation contributing to mirrortemperature measurement or thermal actuation fulfills the foregoingangle condition, it is possible to use a suitable angle-discriminatingoptical system in order to suitably limit the angle range—for example atthe location of a sensor used for mirror temperature measurement.

In an embodiment the electromagnetic radiation in question is of awavelength for which the mirror is at least region-wise opaque. Inparticular the electromagnetic radiation is preferably of a wavelengthof at least 2.5 μm, further particularly a wavelength of at least 5 μm,as can be implemented for example by way of a so-called low-temperatureradiating mechanism at temperatures of up to 400° C., in particular inthe range of up to 200° C.

That wavelength range corresponds at the same time to the relevantwavelength range of the main radiation component of typical mirrormaterials used in EUV lithography such as glass materials which anextremely low coefficient of expansion or (almost) zero expansion(=“ultra low” or “zero expansion” glass). Such a mirror substratematerial is for example the glass ceramic which is marketed by SCHOTTGlass under the trade mark name Zerodur®. A further material which canbe used is for example silicon carbide.

In the aforementioned wavelength range of at least 5 μm that at the sametime guarantees that the wavelengths are outside the transmission windowof the mirror substrate materials in question (which typically includeswavelengths below 4 μm). That accordingly prevents electromagneticradiation from the exterior or from the optical system, in the form ofbackground radiation, from passing through the mirror substrate materialinto the access passage and adversely affecting mirror temperaturemeasurement or thermal actuation. Furthermore, with the wavelength rangeabove 5 μm, it is precisely that range in which a thermopilesensor—which according to the disclosure can be used to particularadvantage—responds or has maximum sensitivity, that is advantageouslyemployed.

That situation is diagrammatically shown in FIG. 2, wherein thetransmission window of the “zero expansion glass” in question isidentified by “I” and the sensitivity window of a thermopile sensor isidentified by “II”, and wherein the curves shown in the drawingrespectively give the spectral radiation density (in watt/(m*m²*sr)) forblack body radiation at temperatures of between 20° C. and 200° C. (insteps of 20° C.).

In an embodiment the access passage is separated from the opticaleffective surface by a remaining mirror material portion, the thicknessof which is in the range of between 5 and 20 mm. In that way for examplein the case of mirror temperature measurement it is possible toimplement a response time (corresponding to the delay between heat inputand a corresponding reaction from the sensor) which is sufficientlyshort for good regulating performance. On the other hand (due to thespacing which is not too low and which preferably is not below 5 mm) itis possible to achieve a desired averaging effect with respect toexisting local variations in the thermal load at the optical effectivesurface, with which corresponding unwanted fluctuations are averagedout.

In an embodiment the access passage extends from the surface of themirror, that is opposite to the optical effective surface, in thedirection of the optical effective surface. The disclosure however isnot limited thereto so that in further embodiments the access passagecan also extend from another surface of the mirror, that does notcorrespond to the optical effective surface, into the mirror (forexample if that is appropriate by virtue of the mirror position in theoptical system, for reasons of structural space).

The disclosure can equally be used in the illumination system or in theprojection objective of a microlithographic projection exposureapparatus, in particular in a microlithographic projection exposureapparatus designed for EUV.

In an embodiment the arrangement further has a regulating device, by wayof which the mirror can be heated to a constant temperature or atemporally variable presetting temperature in dependence on the mirrortemperature measurement.

That temperature can be in particular in the range of between 22° C. and45° C., further particularly in the range of between 25° C. and 40° C.Furthermore that temperature can correspond to the so-called zerocrossing temperature at which there is no or only a negligible thermalexpansion of the mirror substrate material so that heat inputs into themirror substrate material which occur in the lithography process andwhich are possibly non-homogenous do not lead to deformation or opticalaberration phenomena or the aberration phenomena can still be correctedwith an existing correcting mechanism.

In an embodiment the arrangement has a plurality of access passages ofthe above-described kind, whereby, as is described in greater detailhereinafter, it is possible to provide for positionally resolved mirrortemperature measurement and/or thermal actuation.

In an embodiment the arrangement further has at least one heat radiatingmechanism which produces the electromagnetic radiation which ispropagated within the access passage (in particular reflected aplurality of times).

In an embodiment the arrangement can further have a manipulator forvarying the advance position of the heat radiating mechanism along theaccess passage. In that way the heated zone at the mirror (in particularin the region of the optical effective surface of the mirror) andtherewith a (counter)-deformation finally achieved by the thermalactuation according to the disclosure can be varied so that a furtherdegree of freedom with respect to thermal actuation of the mirror inrelation thereto is achieved.

The heat radiating mechanism can be in the form of a heating bar of apreferably substantially needle-shaped geometry, which is advantageousin particular in regard to the comparatively small structural spaceinvolved.

In an embodiment the arrangement has at least two access passages ofdiffering geometry.

In an embodiment at least one access passage can have a geometrydiffering from a cylindrical geometry. Such a geometry can, e.g., be aconical geometry. The disclosure however is not limited thereto, soother geometries, such as for example a step-wise variation of thediameter of the respective access passage, are also possible. Suchgeometries can be advantageous if for example a desired effect in agiven (edge) region of a mirrors, e.g., of a facet mirror, can be betterachieved when using, e.g., a conical access passage than when using anaccess passage of cylindrical geometry.

In an embodiment the at least one heat radiating mechanism is alsolaterally actuable with respect to the direction of the access passage.

The heat radiating mechanism can be connected to a regulatable heatingdevice. The temperature set by such a regulatable heating device forheating the mirror substrate, alternatively or additionally to theadvance position of the heat radiating mechanism, forms a furtherparameter for variation in the thermal actuation of the mirror.

The heat radiating mechanism can involve a low-temperature radiatingmechanism (involving a temperature in the range of up to 400° C.) or ahigh-temperature radiating mechanism (involving a temperature above 400°C.). In addition it is also possible to use monochromatic light sources(for example in the form of lasers or LEDs) as a heat radiatingmechanism.

In an embodiment the arrangement has a plurality of such heat radiatingmechanisms which are arranged as an array and are selectively actuable.

In an embodiment the arrangement further has a cooler for dissipatingheat to the environment. That cooler can be in particular at a constanttemperature. By combining the constant heat dissipation flow caused bysuch a cooler with a heat input which is selectively controllable by wayof the arrangement of low-temperature radiating mechanism, it ispossible to provide an arrangement which is particularly efficient interms of regulating procedures and which permits in particular a fastreaction to non-homogenous heat inputs in the mirror by specificallytargeted variation in the heat radiation emitted by the low-temperatureradiating mechanism.

The disclosure further concerns a method of mirror temperaturemeasurement and/or thermal actuation of a mirror in a micro lithographicprojection exposure apparatus. For preferred configurations oradvantages of the method attention is directed to the foregoinginformation in relation to the arrangement according to the disclosure.

In an embodiment the electromagnetic radiation is produced by way of anarrangement of selectively actuable heat radiating mechanisms. Here toothe heat radiating mechanisms can be low-temperature radiatingmechanisms (involving a temperature in a range of up to 400° C.) orhigh-temperature radiating mechanisms (involving a temperature above400° C.). It is also possible to use monochromatic light sources (forexample in the form of lasers or LEDs) as heat radiating mechanisms.

According to further aspects, the disclosure also relates to anarrangement for thermal actuation of a mirror in a microlithographicprojection exposure apparatus, wherein the mirror has an opticaleffective surface and at least one access passage extending from asurface of the mirror, that does not correspond to the optical effectivesurface, in the direction of the effective surface, wherein thearrangement is designed for thermal actuation of the mirror viaelectromagnetic radiation which is propagated in the access passage,wherein the arrangement further has at least one heat radiatingmechanism which produces the electromagnetic radiation which ispropagated in the access passage, and wherein the heat radiatingmechanism is actuable along the access passage.

In an embodiment, the arrangement has a manipulator for varying theadvance position of the heat radiating mechanism along the accesspassage.

In an embodiment, the heat radiating mechanism is in the form of aheating bar with a preferably substantially needle-shaped geometry.

In an embodiment, the mirror has a plurality of such access passages.

In an embodiment, the arrangement has a plurality of such heat radiatingmechanisms which are arranged as an array.

In an embodiment, the heat radiating mechanisms are selectivelyactuable.

In an embodiment, the mirror is composed of a multiplicity of mirrorfacets.

In an embodiment, each one of the mirror facets has at least one accesspassage with a heat radiating mechanism being actuable along the accesspassage.

In an embodiment, the mirror has at least two access passages ofdiffering geometry.

In an embodiment at least one access passage has a geometry differingfrom a cylindrical geometry, in particular a conical geometry or astep-wise variation of the diameter along the respective access passage.

In an embodiment the at least one heat radiating mechanism is alsolaterally actuable with respect to the direction of the access passage.

In an embodiment the at least one heat radiating mechanism is connectedto a regulatable heating device.

In an embodiment the arrangement further has a cooler for dissipatingheat to the environment.

According to further aspects, the disclosure also relates to a method ofthermal actuation of a mirror in a microlithographic projection exposureapparatus, wherein the mirror has an optical effective surface and atleast one access passage extending from a surface of the mirror, thatdoes not correspond to the optical effective surface, in the directionof the optical effective surface, and wherein the thermal actuation ofthe mirror is effected by electromagnetic radiation which is propagatedin the access passage, wherein the heat radiating mechanism is actuablealong the access passage. The wording according to which “the heatradiating mechanism is actuable along the access passage” also includesembodiments in which the position of the heat radiating mechanism isvariable only along a portion of the access passage (e.g., by varyingthe advance position of the heat radiating mechanism along a partiallength of the access passage).

In an embodiment a counter-deformation achieved via the thermalactuation of the mirror at least partially compensates a thermal surfacedeformation of the mirror due to absorption of radiation emitted by alight source in operation of the microlithographic projection exposureapparatus.

In an embodiment the electromagnetic radiation is produced by way of anarrangement of selectively actuated heat radiating mechanism.

In an embodiment the heat radiating mechanisms are thermally actuateddifferent from each other along a cross-section of the mirror.

In an embodiment the mirror is composed of a multiplicity of mirrorfacets.

In an embodiment at least two, in particular all of the mirror facetsare thermally actuated different from each other via the heat radiatingmechanism.

Further configurations of the disclosure are to be found in thedescription and the appendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is described in greater detail hereinafter viaembodiments by way of example illustrated in the accompanying drawings,in which:

FIG. 1 shows a diagrammatic view of an arrangement according to thedisclosure for mirror temperature measurement in a first embodiment ofthe disclosure,

FIG. 2 shows a graph representing the wavelength dependency of thespectral radiation density (in watt/(m*m²*sr)) for differenttemperatures together with the transmission window of a typical mirrorsubstrate material and the sensitivity window of a typical thermopilesensor,

FIGS. 3-4 show diagrammatic views and arrangements for mirrortemperature measurement in further embodiments of the disclosure,

FIGS. 5-6 show diagrammatic views of different concepts for thermalactuation of a mirror, and

FIGS. 7-13 show diagrammatic views of arrangements for thermal actuationof a mirror in accordance with different embodiments of the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter reference will firstly be made to FIG. 1 to describe anarrangement according to the disclosure for mirror temperaturemeasurement in a first embodiment.

FIG. 1 diagrammatically shows a mirror 101 whose optical effectivesurface is identified by reference 101 a, wherein the side surface ofthe mirror substrate is identified by reference 101 b and the surfaceremote from the optically effective surface 101 a, or rear side of themirror, is identified by reference 101 c. Extending into the mirrorsubstrate of the mirror 101 is an access passage 110 which for exampleis in the form of a bore and whose end face, that is towards theoptically effective surface 101 a of the mirror 101 is identified byreference 110 a and whose side surface or wall is identified byreference 110 b. Disposed on the optically effective surface 101 a ofthe mirror 101 is a reflective coating (not shown in FIG. 1).

FIG. 1 like also the other Figures represents a diagrammatic view whichis not true to scale, wherein purely exemplary dimensions of the accesspassage 110 (without the disclosure being restricted thereto) caninclude a diameter for the bore in the range of between 5 and 20 mm anda spacing, identified “d”, of the end face 110 a from the opticaleffective surface 101 a in the range of also between 5 and 20 mm.Typical thicknesses of the mirror 101 itself can be (also only by way ofexample and without restriction on the disclosure) for example in therange of between about 50 mm and 120 mm.

The arrangement shown in FIG. 1 further includes a tube 120 whichprojects from the region outside the mirror 101 into the access passage110. The spacing identified by “a” of the end portion of the tube 120from the end face 110 a of the access passage 110 (also without thedisclosure being restricted thereto) can be for example at least 3 mm(in the case of an actuated mirror) or at least 0.5 mm (in the case of anon-actuated or stationary mirror). Corresponding values by way ofexample of at least 3 mm in the case of an actuated mirror or at least0.5 mm in the case of a non-actuated or stationary mirror can apply tothe spacing of the wall of the tube 120 from the side wall 110 b of theaccess passage 110.

The arrangement 100 in FIG. 1 further includes a sensor 130 arranged atthe end portion of the tube 120, outside the mirror 101, and in the formof a thermopile sensor in the illustrated embodiment. Such a thermopilesensor in known manner includes a receiver membrane in the form of ablackened surface which is to be irradiated, as well as a chain ofthermocouple elements for amplifying the electrical voltage obtained byconversion of the measured temperature difference. A typical voltageswing involved in that case can be for example 40 μV/K and can befurther amplified by a pre-amplifier 140.

As shown by the broken lines in FIG. 1, in the case of a thermal loadingon the optical effective surface 101 a of the mirror 101 the heatradiation which is read off in the immediate proximity of the opticaleffective surface 101 a, more specifically at the end face 110 a of theaccess passage 110, passes by multiple grazing-incidence reflection atthe wall of the tube 120 to the sensor 130 where the temperature changecaused by the aforementioned loading is ascertained.

To ensure that only that electromagnetic radiation which has beenreflected at the wall of the tube 120 in a condition of grazingincidence is evaluated the sensor 130 can have an angle-discriminatingoptical system in per se known manner. In addition, to ensure that onlyelectromagnetic radiation in the above-described wavelength range above5 μm is evaluated it is possible to use a suitable filter which forexample completely blocks out wavelengths below 5 μm (at which themirror material such as for example the above-mentioned glass materialswith a thermal expansion of almost zero still behaves as transparent).

In further embodiments the structure shown in FIG. 1 can be used notonly for monitoring the mirror temperature but also (using a suitableregulating device) for active regulation of the mirror temperature. Inthat case in particular the mirror 101 can be kept from the outset at atemperature at which any temperature gradients at the mirror surface(for example as a consequence of non-homogenous heat loads as can becaused by special illumination settings) are not reproduced in terms ofdeformation of the mirror substrate material. In that respect it ispossible to make use of the fact that the coefficient of thermalexpansion (in units of m/(m*K)), in its temperature dependency, has azero crossing, in the area around which no or only negligible thermalexpansion of the mirror substrate material occurs.

That temperature is also referred to as the zero crossing temperature.The zero crossing temperature can be set by the material manufactureraccording to the desired properties of the thermal design, typicalvalues being between 22° C. and 40° C. That aspect will be discussed ingreater detail hereinafter in connection with thermal actuationaccording to the disclosure and with reference to FIG. 5 ff.

As a further embodiment for mirror temperature measurement FIG. 3 showsa structure which is basically similar to FIG. 1, wherein componentswhich correspond to each other or which involve substantially the samefunction are denoted in comparison with FIG. 1 by references increasedby “200”. The arrangement in FIG. 3 differs from that in FIG. 1 in thatthe sensor 330 is not placed outside the mirror 301 but in the immediateproximity of the end face 310 a of the access passage 310. For thatpurpose, instead of the tube 120 in FIG. 1, it is possible to provide asimilar component 320 which however is provided with an end carrier orroof portion 320 a, on which the sensor 310 is disposed. That structurehas the advantage over the FIG. 1 structure that conversion of theelectromagnetic radiation read off at the location of the end face 310 aof the access passage 310 into electrical voltage is already effected inthe immediate proximity of that end face 310 a so that only theelectrical voltage still has to be transported through the accesspassage 310. As shown in FIG. 3 suitable electric lines 325 are passedfor that purpose to the pre-amplifier 340.

FIG. 4 shows a further embodiment of an arrangement according to thedisclosure for mirror temperature measurement, wherein in comparisonwith the FIG. 1 arrangement components which are similar or involvesubstantially the same function are identified by references increasedby “300”.

The arrangement 400 in FIG. 4 differs from the arrangement 100 in FIG. 1in that, dispensing with a tube within the access passage 410, its wall410 b itself is made sufficiently reflective by polishing or the like sothat the mirror substrate of the mirror 401 performs the function of alight waveguide that was implemented by the tube 120 in FIG. 1, byvirtue of the reflective configuration of that wall 410 b itself. Inregard to the appropriate spacings, dimensions and reflection anglereference is directed to the above-described embodiments. In thearrangement in FIG. 4, similarly to the above-described embodiments, useis made of the fact that, with respect to the electromagnetic radiationincident at the sensor 430, the emission component from the wall 410 bof the access passage 410 is negligible in comparison with the radiationcomponent which is transported “forwardly” along the access passage 410and transported from the location of the radiation reading operation atthe end face 410 a of the access passage 410 so that it is not forexample an average temperature over the entire bore that is measured,but in this case also substantially the temperature at the end face 410a, that is to say in the immediate proximity of the optical effectivesurface of the mirror 410. A background component which possiblyremains, by virtue of a radiation emission from the wall of the bore ofthe access passage 410, can be eliminated in this case as in theabove-described embodiments by way of suitable correction models.

The aspect according to the disclosure of actuation of a mirror in amicro lithographic projection exposure apparatus is discussedhereinafter. Firstly in that respect different concepts regardingthermal actuation will be described with reference to FIGS. 5 and 6.

The diagrammatic views in FIG. 5 show the respective heat flows orinputs into the mirror element 501 indicated by arrows for thenon-operative condition (FIG. 5 a) and the condition during waferexposure (FIG. 5 b), wherein A denotes the heat input due to absorbedEUV light (which disappears for the non-operative condition of theprojection exposure apparatus), B denotes heating power introduced (forexample using a regulator, employing the mirror temperature measurementof FIGS. 1-4), C denotes the resulting overall heat input at the opticaleffective surface of the mirror 501, D denotes the heat flow within themirror element 501 and E denotes the heat dissipation flow from themirror element 501 to a cooler 550.

It will be seen from FIG. 5 b that a non-homogenous thermal loading onthe mirror 501 (for example involved with specific illuminationsettings) admittedly leads to local temperature non-homogeneities orgradients within the mirror element 501, but in that respect thosetemperature non-homogeneities, as already explained hereinbefore, do nothave any significant effects on mirror deformation phenomena or opticalproperties of the arrangement as long as thermal regulation is effectedusing the heating power B to a suitable temperature in the region of thezero crossing temperature.

If however the temperature gradient which is set in the mirror 501 asdescribed departs from the range that is still acceptable around thezero crossing temperature, deformation of the mirror 501 and opticalaberration phenomena can be the result. To compensate for that, as shownin FIG. 6 b a heat input profile B which is complimentary to thenon-homogenous heat input by virtue of the absorbed EUV light A isgenerated via a two-dimensional heating device, with the consequencethat the total resulting condition C again corresponds to a homogenousheat input (without temperature gradients in the mirror 601). For thatpurpose, unlike FIG. 5, a thermal actuator which is actuable intwo-dimensionally variable fashion or in positionally resolved manner isused, as is described hereinafter with reference to FIG. 7.

Different embodiments of an arrangement according to the disclosure forthermal actuation of a mirror are described hereinafter with referenceto FIGS. 7 and 8.

FIG. 7 firstly shows a diagrammatic view of a mirror 700 having aplurality of access passages 710, 711, 712, . . . which, similarly tothe access passage 110 and 310 in FIG. 1 and FIG. 3 respectively extendfrom the rear side of the mirror in the direction towards the opticaleffective surface 701 a of the mirror 701. The reflective layer in theregion of the optical effective surface 701 a of the mirror is hatchedin FIG. 7 (and FIG. 8) and is shown only diagrammatically and on anexaggerated scale.

Also in a fashion corresponding to the embodiments of FIGS. 1 and 3,extending into the access passages 710, 711, 712, . . . are respectivetubes 720, 721, 722, . . . . In regard to suitable dimensions orspacings by way of example of the access passages 710, 711, 712, . . .from the optical effective surface 701 a of the mirror 701 reference ismade to the description relating to FIGS. 1 and 3 respectively.

Unlike the embodiments of FIG. 1 ff intended for mirror temperaturemeasurement, as shown in FIG. 7 no sensor is arranged at the end portionof the access passages 710, 711, 712, . . . outside the mirror 701, butin each case there is a low-temperature radiating mechanism 760, 761,762, . . . which produces a heat radiation with a maximum in radiationdensity in the range of between 5 and 10 μm as a black body radiatingmechanism involving a temperature in the range of up to 400° C.,typically in the range of between 100° C. and 200° C. In furtherembodiments, instead of the low-temperature radiating mechanism, it isalso possible to use a high-temperature radiating mechanism (involving atemperature above 400° C.) or also monochromatic light sources (forexample in the form of lasers or LEDs) as a heat radiating mechanism.

The heat radiation produced by the low-temperature radiating mechanisms760, 761, 762, . . . passes through the respective access passages 710,711, 712, . . . (similarly to FIGS. 1, 3 and 4 but now in the reversedirection) and goes to the end face 710 a, 711 a, 712 a, . . . towardsthe optical effective surface 701 a, of the respective access passage710, 711, 712, . . . , wherein as in the above-described embodiments itis reflected at the respective wall of the access passage 710, 711, 712,. . . , in grazing incidence with a low reflection angle (preferably notgreater than 20°, further preferably not greater than 15°). In thatrespect the reflection angle is interpreted here and hereinafter as theangle of the incident and reflected beam relative to the reflectingsurface (identified by ‘α’ in FIG. 7).

In this case on the one hand the grazing incidence provides that thepredominant proportion of the heat radiation reaches the aforementionedend face 710 a, 711 a, 712 a, . . . of the respective access passage710, 711, 712, . . . while an absorption proportion at the wall of therespective access passage 710, 711, 712, . . . is negligibly slight. Onthe other hand once again the wavelength of the heat radiation isadvantageously in the range in which the mirror substrate material, forexample the above-mentioned glass materials with a thermal expansion of(almost) zero, is practically opaque, so that the heat radiation can beeffectively coupled in to the mirror substrate material in the immediateproximity of the optical effective surface 701 a.

As can also be seen from FIG. 7 a respective separate actuatingmechanisms 760 a, 761 a, . . . is associated with each low-temperatureradiating mechanism 760, 761, . . . so that the entire arrangement oflow-temperature radiating mechanisms 760, 761, . . . (which isconstructed in the form of an array in matrix shape) is selectivelyactuable, in order to provide a two-dimensional positionally resolvedheat input into the mirror 700 similarly to FIG. 6 (but from the rearside of the mirror) and in that way to take account of theabove-described local non-homogeneities (caused for example by givenillumination settings) of the temperature distribution on the mirror701.

In addition a component part of the arrangement 700 in FIG. 7 is acooler 750 having a plurality of cooling passages 751 which each have arespective cooling medium 752 flowing therethrough. The cooler 750serves for permanent dissipation of heat to the environment and is at aconstant temperature (in which respect temperature values by way ofexample, without the disclosure being restricted thereto, can be in therange of 22° C. down to typical cryogenic temperatures such as forexample 77 Kelvin (when using for example liquid nitrogen)). In thatway, that is to say as a result of the combination of the cooler 750providing a constant heat discharge flow with a controllable heat inputby way of the arrangement of low-temperature radiating mechanisms 760,761, . . . , an arrangement which is particularly efficient in terms ofregulating procedures is embodied, which in particular permits areaction which is fast in terms of regulating procedure tonon-homogenous heat inputs in the mirror 701 by a correspondingvariation in the heat or infrared radiation emitted by thelow-temperature radiating mechanisms 760, 761, . . . .

As in the above-described embodiments the arrangement of FIG. 7 alsoavoids mechanical contact of the components used with the mirror 701. Inaddition, disturbance of the mirror surroundings is avoided by virtue ofthe fact that thermal actuation is effected only within the arrangement700 or only the cooler 750 (which is constant in its temperature) isperceived from the exterior, in which respect in particular no straylight passes into the system.

The components in the arrangement in FIG. 7, namely the cooler 750 onthe one hand and the arrangement including the low-temperature radiatingmechanisms 760, 761, . . . on the other hand can be operatedsimultaneously on the one hand. The cooler 750 and the arrangementincluding low-temperature radiating mechanisms 760, 761, . . . canhowever also be operated independently of each other, or switched off.In other words, it is also possible to implement exclusively heating ora feed of heat radiation to the end faces 711 a, . . . of the accesspassages without simultaneously cooling, or it is possible to implementonly dissipation of heat radiation from the end faces 711 a, . . . ofthe access passages to an external cooler or a reservoir, as isdescribed in greater detail hereinafter with reference to FIG. 9 ff.

By virtue of the described properties of thermal neutrality relative tothe exterior and also the avoidance of disturbing the optical effectivesurface 701 a of the mirror 701, the structure shown in FIG. 7 issuitable for being coupled so-to-speak as a module to a(interferometric) measurement structure which is typically used duringmanufacture (=“metrology tool”) so that measurement of the mirror 701which is effected by such a structure during manufacture can already beimplemented in the thermal condition in which the mirror 701 is alsooperated in the subsequent actual lithographic process. In that respectit is also possible to already implement corresponding temperaturegradients which occur in the subsequent lithography process in themirror 701 (for example by virtue of given illumination settings) inorder to avoid corresponding transfer errors in making the transitionfrom manufacture to operation.

Although described hereinbefore in relation to thermal actuation, theconcept, illustrated with reference to FIG. 7, of a plurality of accesspassages 710, 711, 712, . . . can also be used in the mirror temperaturemeasurement described with reference to FIGS. 1, 3 and 4 so that thiscan also be implemented in positionally resolved relationship (forexample with a two-dimensional array of access passages withrespectively associated sensors).

In further embodiments, a heating principle similar to FIG. 3 can alsobe used in a modification to FIG. 7, wherein low-temperature radiatingmechanisms 760, 761, . . . are placed in the immediate proximity of theend faces 710 a, 711 a, 712 a, . . . of the respective access passages710, 711, 712, . . . .

FIG. 8 shows a further embodiment, wherein, in comparison with FIG. 7,corresponding elements or elements involving substantially the samefunction are identified by references increased by “100”. Thearrangement 800 differs from the arrangement 700 in FIG. 7 in that,instead of the plurality of low-temperature radiating mechanisms 760,761, . . . there is only a single low-temperature radiating mechanism860 which however is of a correspondingly large surface area and whichrepresents a thermally actuable or heatable plate (once again in theform of black body), whose emitted heat radiation passes into the accesspassages 810, 811, . . . distributed by way of the mirror 801 on therear side 801 c thereof and—in this respect similarly to FIG. 7—passesafter grazing incidence reflection at the walls of the tubes 820, 821, .. . to the respective edge portions 810 a, 811 a, . . . of the accesspassages 810, 811, and is thus coupled into the mirror substratematerial in the immediate proximity of the optical effective surface 801a of the mirror 801. Here too, in further embodiments, instead of thelow-temperature radiating mechanism 860, it is also possible to use ahigh-temperature radiating mechanism (involving a temperature above 400°C.) or also a monochromatic light source (for example in the form oflasers or LEDs) as the heat radiating mechanism.

In a further aspect the access passages which are present in accordancewith the disclosure within the mirror can be used to implement passivecooling of the optical effective surface of the mirror by way ofdirected emission of heat radiation. FIG. 9 serves to illustrate thatprinciple, which in turn shows a mirror 900 which in the illustratedembodiment is in the form of a facet mirror composed of a plurality ofmirror facets 910, 902, 903, wherein there are provided access passages911, 912, 913 (in the embodiment, in each of the mirror facets). In thatarrangement the mirror can be of a similar composition to the otherembodiments according to the disclosure, and also in the form of anindividual mirror (for example an imaging mirror in the opticalprojection system). The mirror facets can be adapted to be individuallyactuable, without the disclosure be restricted thereto, as indicated bythe double-headed arrows P1 and P2 shown in FIG. 9.

As is diagrammatically shown in FIG. 9 the IR radiation which isproduced upon heating of the optically effective surfaces 901 a, 902 a,903 a of the mirror 900 (and which typically is of a wavelength in therange of between 0.8 μm and 1000 μm) is propagated along the accesspassages 911, 912, 913 and goes to a reservoir 940 by way of which theIR radiation is dissipated. That is effected as shown in FIG. 9 withoutthe presence of cooling fingers engaging into the access passages 911,912, 913, that is to say solely utilizing the directed emission of theIR radiation along the access passages 911, 912, 913 which act as waveguides for the IR radiation. That accordingly provides for passivecooling at a comparatively low level of structural complication.

In regard to suitable dimensions and sizes by way of example for theaccess passages 911, 912, 913 (in particular in relation to theirlateral extent and the spacing of the end faces, that are towards therespective optical effective surfaces 901 a, 902 a, 903 a of the mirrorfacets 901, 902, 903, of the access passages 911, 912, 913 relative tothe respective optical effective surface 901 a, 902 a and 903 a and inregard to the resulting reflection angles of the IR radiation),attention is directed to the embodiment described hereinbefore withreference to FIGS. 1-8. The efficiency of passive cooling depends on theone hand on the temperature of the reservoir 940 (the lower thattemperature, the correspondingly more effective is the passive cooling),and on the other hand on the area which the access passages occupy. If,just by way of example, the proportion of the cross-sectional area ofall access passages 911, 912, 913 in relation to the totalcross-sectional area of the rear side of the mirror is assumed to beabout 50% and if in addition just by way of example heating of theoptical effective surface 901 to a temperature of about 40° C. and areservoir temperature of 0° C. are considered, it is possible to achievea reduction in temperature via the passive cooling by a value of theorder of magnitude of 1-2° C. per hour.

As indicated in FIG. 10 a the insides or walls of the access passages911, 912, 913 can be of a reflecting nature, that is to say they can beprovided with a reflecting coating or mirroring 911 b, 912 b, 913 b.

In addition the access passages can have different degrees of emissivityin the region of their end faces and their side surfaces or walls (forexample, by the end faces of the access passages being blackened and theside surfaces or walls of the access passages being mirrored for examplewith silver or silver iodide). The end faces of the access passages 911,912, 913 can thus be designed—for example by a suitable anti-reflectionlayer for IR radiation (that is to say a strongly absorbent layer whichfor example has a maximum in the absorption spectrum in the range of10-20 μm)—with an emissivity of close to 1 while the side surfaces orwalls of the access passages can have an emissivity of close to 0.Preferably moreover the mirror rear side (that is to say the surfaceopposite to the optical effective surface) is mirrored in order toprevent the rear side of the mirror cooling down excessively greatly asa consequence of radiation exchange between the mirror material and thereservoir 940 which is at a lower temperature, and to prevent anunwanted temperature gradient from occurring in the mirror material.

The above-described configuration can contribute to for example theabove-described passive cooling of the optical effective surface of themirror being effected by way of directed emission of heat radiationsubstantially or predominantly only from the end faces of the accesspassages (or for the optical effective surface transmitting heat tothose end faces), but not or to a considerably lesser degree from theside surfaces or walls of the access passages. In other words, it ispossible in that way to ensure that local cooling of the mirror materialin the region of the side surfaces or walls does not become excessive ordependent on the material surrounding the respective access passage sothat cooling is effected substantially only in the region of the endfaces of the access passages and thus only in the proximity of theoptical effective surface of the mirror.

As diagrammatically illustrated in FIG. 10 b a plurality of accesspassages 911, 912, 913, . . . can be arranged in a two-dimensionalarray. The access passages 911, 912, 913, . . . can basically be of across-section of any geometry (for example round or rectangular). In theFIG. 10 b embodiment the access passages 911, 912, 913, . . . are of ahoneycomb (for example hexagonal) geometry, which is advantageous inregard to mechanical strength or stability as it is still possible toachieve adequate strength for the mirror facets 901, 902, 903 even withthe access passages 911, 912, 913, . . . involving a comparatively highproportion in relation to the total volume of the respective mirrorfacet 901, 902, 903. As indicated in FIG. 10 c the respective mirrorfacets 901, 902, 903 in plan view can have a smooth and steadilyextending surface or optical effective surface.

A further embodiment of the disclosure is described hereinafter withreference to FIG. 11. The FIG. 11 configuration differs from that shownin FIG. 9 in that, instead of the reservoir 940 for dissipation of theIR radiation, there is an arrangement 945 (preferably once again in theform of an array or matrix) including a heat radiating mechanism in theform of an IR diode laser array. The heat radiation generated by thediode lasers 946 of the arrangement 945, similarly to FIG. 7, passesthrough the respective access passages 911, 912, 913 and goes to the endface, towards the optical effective surface 701 a, of the respectiveaccess passage 911, 912, 913, wherein it is grazingly reflected as inthe above-described embodiments at the respective wall of the accesspassage 911, 912, 913.

The embodiment of FIG. 11 can be of a substantially similarconfiguration to the embodiment of FIG. 7, wherein, in particularsimilarly to FIG. 7, the individual heat radiating mechanisms or IRdiode lasers of the arrangement 945 can be selectively actuable in orderto provide for a locally targetedly variable input of heat into therespective mirror facet 901, 902, 903, depending on the respectivespecific factors involved. The FIG. 11 configuration differs from thatshown in FIG. 7 however—apart from the application to a facet mirrorwhich is implemented in FIG. 11—in that, as shown in FIG. 11, thearrangement does not involve simultaneous cooling (as is effected in thearrangement in FIG. 7 by the cooler 750), that is to say the arrangementexclusively involves heating of the respective mirror facet 901, 902,903. In other respects, attention is directed to the embodimentsdescribed hereinbefore with reference to FIGS. 1-10 in regard tosuitable dimensions and sizes by way of example for the access passages911, 912, 913 and the resulting reflection angles of the IR radiation.

Further embodiments of actuators relating to the thermal characteristicsof a mirror are described hereinafter with reference to FIGS. 12 and 13.In this respect once again, in comparison with FIG. 8, correspondingelements which are comparable with respect to their function are denotedby reference numerals increased by ‘100’.

The mirror 901 can be an individual mirror (for example an imagingmirror in the optical projection system) or also a facet mirror which iscomposed of a multiplicity of mirror elements. Furthermore, a pluralityof heat radiating mechanisms/access passages can be realized both for afacet mirror being composed of a multiplicity of mirror elements and asingle mirror (e.g., a relatively large-sized mirror).

In the FIG. 12 embodiment a heating bar 960 serves as the temperatureradiating mechanism, which heating bar is substantially needle-shaped inthe illustrated embodiment (and thus takes up only a small amount ofspace) and is mounted displaceably along an access passage 910 in themirror 901—along the z-axis in the illustrated co-ordinate system—. Bydisplacement of the heating bar 960 the heated zone at the mirror 901(in particular in the region of the optical effective surface 901 a ofthe mirror 901) and thus the (counter)-deformation achieved finally viathe thermal actuation according to the disclosure can be varied. Thus itwill be readily apparent that for example placement of the heating bar960 in the initial portion of the access passage 910, that is remotefrom the optical effective surface 901 a of the mirror 910, leads to atemperature gradient occurring in the mirror substrate material, that isdifferent from advance movement thereof into the immediate proximity ofthe end face 910 a of the access passage 910. Therefore thedisplaceability of the heating bar 960 provides a further degree offreedom with respect to thermal actuation of the mirror 901 in relationthereto.

Displacement of the heating bar 960 can be from a position in theimmediate proximity of the end face 910 a of the access passage 910 intothe region outside the access passage 910. Typical displacement travels(without the disclosure being restricted thereto) can be of the order ofmagnitude of 0-30 mm, the value 0 mm corresponding to the beginning ofthe access passage 910 on the side that is remote from the opticaleffective surface 910 a. In that respect the displacement travel of theheating bar 960 can extend in particular to directly in front of (forexample to a distance of 1 mm from) the end portion 910 a of the accesspassage 910, in which case, as in the above-described embodiments,direct mechanical contact in relation to the mirror material is avoidedin order not to apply any unwanted mechanical deformation to the mirror901.

The heating bar 960 is heated up by way of a heating device 970 and actsas a black body radiator, emitting heat in all spatial directions. Theheating temperature of the heating bar 960 can be for example in therange of between 60° C. and 350° C. (without the disclosure beingrestricted thereto). An insulator plate 980 which can be made forexample from a suitable ceramic material prevents an unwantedtransmission of heat radiation from the heating device 970 to the mirror901. Besides the advance position of the heating bar 960, thetemperature set by the heating device 970 for heating the mirrorsubstrate forms a further parameter for variation in thermal actuationof the mirror 901.

A possible mode of operation of the FIG. 12 arrangement will now bedescribed.

The arrangement of FIG. 12 can be used to influence the imagingcharacteristics of the mirror 901 by thermal actuation with variableheating of the mirror 901. The measurement technology used in this casemay involve a measuring device which directly measures the wave frontissuing from the mirror 901. In the case of a mirror 901 in the form ofa facet mirror made up of a multiplicity of mirror elements, theresulting wave front is produced by overlapping of the individualcontributions of those mirror elements.

With knowledge of the behaviour of the mirror 901 when heating occurs itis then possible to react to changes in the wave front in the field bythermal actuation according to the disclosure.

In practice in that respect, to characterize the behaviour of thearrangement of FIG. 12 when heating is effected for a plurality of (forexample two hundred) different heating processes of the mirrorsubstrate—via simulation or by measurement—it is possible in each caseto provide for determining the wave front coming from the mirror 901 inorder to ascertain the change in the wave front, which is respectivelyachieved by the heating in question. Those heating processes for themirror substrate can in that case differ from each other as describedhereinbefore with respect to the temperature set by the heating device970 and/or with respect to the advance position of the heating bar 960.In that case the time dependency of the temperature gradient whichoccurs in the mirror substrate material or the variation with respect totime of the deformation which ultimately occurs with respect to themirror 901 can also be taken into consideration and evaluated.

The results obtained in that calibration operation can be stored forexample in a suitable table and can be used in operation of the systemto ascertain which heating process is the most suitable for a givenmeasured wave front, to produce a suitable counter-deformation.

If now, for a given radiation loading with respect to the mirror 901 inoperation of the system, the deformation of the optical effectivesurface 901 a, that occurs in that case in relation to time withoutthermal actuation, it is then possible to precisely select a givenheating or actuation mode, on the basis of the data recorded in thecalibration operation, in such a specific fashion as to afford anopposite action or a compensation effect.

The thermal behaviour of the mirror 901 can be characterized inparticular by way of FEM simulation operations (FEM=‘finite elementmethod’) in order on the one hand to ascertain which deformations arecaused by a given radiation loading on the mirror in operation of thesystem and which thermal actuation (in the sense of ‘counteractingheating’) is suitable for compensating for such deformation phenomena.If for example the wave front measurement performed in operation of thesystem gives an unwanted triple-waviness then the heating suitable foreliminating that triple-waviness can be ascertained from the datapreviously recorded in the calibration process.

In further embodiments it is also possible to select other geometriesfor the access passage, for example as diagrammatically illustrated inFIG. 13, a conical geometry of the access passage 910′ in order toachieve a different behaviour in relation to time of the temperaturegradient in the mirror substrate material or the material expansion thatis involved therewith.

In addition individual mirrors of a facet mirror can also be constructedwith access passages of differing geometry. By way of example inembodiments of the disclosure some individual mirrors of a facet mirrorcan each involve an access passage 910′ of conical geometry (if forexample a desired effect in a given (edge) region of the facet mirrorcan be better achieved when using a conical access passage 910′ thanwhen using a cylindrical access passage 910), and others with an accesspassage of cylindrical geometry. Other geometries, such as for example astep-wise variation of the diameter along the respective access passage,are also possible. Other geometries, such as for example a step-wisevariation of the diameter along the respective access passage, are alsopossible.

Even if the disclosure has been described by reference to specificembodiments numerous variations and alternative embodiments will beapparent to the man skilled in the art, for example by combinationand/or exchange of features of individual embodiments.

Accordingly it will be appreciated by the man skilled in the art thatsuch variations and alternative embodiments are also embraced by thepresent disclosure and the scope of the disclosure is limited only inthe sense of the accompanying claims and equivalents thereof.

What is claimed is:
 1. An arrangement, comprising: a mirror having an optical effective surface, a second surface different from the optical effective surface, and an access passage extending from the second surface in a direction of the optical effective surface; wherein the arrangement is configured so that: a temperature of the mirror and/or a thermal actuation of mirror is measurable via multiple reflections of electromagnetic radiation within the access passages as the electromagnetic radiation is propagated along the access passage; and the electromagnetic radiation is coupleable via the access passage into a region in immediate proximity of the optical effective surface.
 2. The arrangement of claim 1, wherein a reflection angle of the electromagnetic radiation within the access passage is not greater than 20°.
 3. The arrangement of claim 1, wherein a region of the mirror is opaque to the electromagnetic radiation.
 4. The arrangement of claim 1, wherein the electromagnetic radiation has a wavelength of at least 2.5 μm.
 5. The arrangement of claim 1, wherein the second surface is opposite to the optical effective surface.
 6. The arrangement of claim 1, further comprising a tube projecting into the access passage.
 7. The arrangement of claim 1, wherein the access passage comprises a reflecting coating.
 8. The arrangement of claim 1, wherein an end face of the access passage has a first emissivity, and a side surface of the access passage has a second emissivity which is different from the first emissivity.
 9. The arrangement of claim 1, further comprising a sensor configured to detect the electromagnetic radiation.
 10. The arrangement of claim 9, wherein the sensor comprises a thermopile sensor.
 11. The arrangement of claim 1, further comprising a regulating device by which the mirror is heatable to a constant temperature depending on a mirror temperature measurement.
 12. The arrangement of claim 1, wherein the mirror comprises a plurality of access passages.
 13. The arrangement of claim 1, further comprising a heat radiating mechanism configured to produce the electromagnetic radiation.
 14. The arrangement of claim 13, further comprising a manipulator configured to vary a position of the heat radiating mechanism along the access passage.
 15. The arrangement of claim 13, wherein the heat radiating mechanism comprises a heating bar.
 16. The arrangement of claim 1, wherein the access passage has a geometry differing from a cylindrical geometry.
 17. The arrangement of claim 1, wherein the mirror comprises at least two access passages of differing geometry.
 18. The arrangement of claim 13, wherein the heat radiating mechanism is laterally actuable with respect to the direction of the access passage.
 19. The arrangement of claim 13, wherein the heat radiating mechanism is connected to a regulatable heating device.
 20. The arrangement of claim 13, comprising a plurality of selectively actuable heat radiating mechanisms arranged as an array.
 21. The arrangement of claim 1, further comprising a cooler configured to dissipate heat to the environment.
 22. The arrangement of claim 1, wherein the mirror comprises a multiplicity of mirror facets.
 23. A method of measuring a temperature of a mirror in a microlithographic projection exposure apparatus and/or thermally actuating the mirror, the mirror having an optical effective surface, a second surface, and an access passage extending from the second surface in a direction of the optical effective surface, the method comprising: reflecting electromagnetic radiation a plurality of times within the access passage as the electromagnetic radiation propagates along the access passage to effect the mirror temperature measurement of the mirror and/or thermal actuation of the mirror, wherein the electromagnetic radiation is coupled by way of the access passage into a region in immediate proximity of the optical effective surface.
 24. The mirror of claim 23, further comprising using an arrangement of selectively actuated heat radiating mechanisms to produce the electromagnetic radiation.
 25. The mirror of claim 23, further comprising using a cooler to maintain a constant heat discharge flow.
 26. A method of thermally treating a mirror in a microlithographic projection exposure apparatus, the mirror having an optical effective surface, a second surface different from the optical effective surface, and an access passage extending from the second surface in a direction of said effective surface, the method comprising: passively cooling the optical effective surface by propagating electromagnetic radiation along the passage to a reservoir and dissipating the electromagnetic radiation from the reservoirs, wherein the electromagnetic radiation occurs as a consequence of heating of the optical effective surface of the mirror.
 27. The method of claim 26, wherein the access passage comprises a reflecting coating.
 28. The method of claim 26, wherein the mirror comprises a multiplicity of mirror facets.
 29. The method of claim 26, wherein the mirror has a multiplicity of access passages.
 30. The method of claim 29, wherein the access passages are of a substantially honeycomb configuration. 